Nov-2024

Biomass and plastic waste gasification: Enabling the energy transition and circular economy (ERTC 2024)

As the demand for lower-carbon and more circular products intensifies, more and more refiners and chemical manufacturers are evaluating the potential benefits of revamping existing gasification units to help enable the energy transition and the plastic circular economy.

Harold Boerrigter and Sven Felske
Shell Catalysts & Technologies

Article Summary

Gasification of hydrocarbon feedstocks to produce syngas and other products is an established process. Now, through the development of pre-conversion technologies, which can process more challenging plastic, biomass, and unsorted waste streams, gasification could prove a pivotal technology for the production of lower-carbon, synthetic biofuels, in addition to helping to significantly increase plastic recycling rates.

Importantly, reconfiguring existing gasification units can be simple and cost-effective. This can help unlock advantaged feeds that cannot be processed by other recycling methods, such as mechanical recycling and chemical recycling with pyrolysis.

The case for change
There is a growing imperative to switch from fossil-based transport fuels, which account for about 20% of global CO₂ emissions, to lower-carbon, bio-based, and synthetic fuels. For example, the EU’s ReFuelEU aviation initiative mandates a progressive increase in the use of sustainable aviation fuels (SAF) and synthetic aviation fuels. By 2035, aviation fuel supplied at EU airports must contain at least 20% SAF – a 900% increase compared with 2025 requirements.

At the same time, the world is generating about 2.1 billion tonnes of solid waste every year, between 5 and 12% of which is plastic. With only 9% of plastic waste recycled each year, legislation and initiatives to tackle plastic waste and increase circularity are becoming central to efforts. For example, the EU has introduced a ban on member states exporting hazardous or hard-to-recycle plastic to non-Organisation for Economic Co-operation and Development (OECD) countries. It set stringent waste-reduction targets, which include increasing its plastic recycling rate to 55% by 2030.

Gasification opportunity
Gasification is an established process that can convert a wide range of mixed municipal, biomass, and unsorted plastic waste and residues into an intermediate product known as syngas. This versatile feedstock  can be used instead of virgin hydrocarbons to produce fuels, electricity, chemicals, and plastic (Figure 1).

Adapting existing gasification units to process waste streams is relatively simple and inexpensive. It provides companies with two key opportunities:
· Biofuels: Companies can leverage significant volumes of low-value sustainable biomass residues, such as those from industrial processes, to produce low-carbon, bio-based fuels with significant margins.
· Circular plastic: Companies can use the growing supply of low-value waste plastic to produce high-value circular plastic products and achieve potentially higher margins.

Pre-conversion for gasification
A key part of the gasification process is pre-conversion, which involves converting the starting biomass and waste into a suitable feedstock for the gasification unit. Pre-conversion involves one of three key processes, depending on the biomass or waste stream used (Figure 2):

1 Fast pyrolysis for woody biomass
Fast pyrolysis – part of the Integrated Shell Biomass Gasification Process, yields pyrolysis oil suitable for gasification in, for example, a Shell liquids gasifier with waste heat recovery. In fact, fast pyrolysis can be deployed in existing liquid/residue gasifiers with only minor adaptions to the feed system. Moreover, because fast pyrolysis is simple and cost-effective to deploy, it can contribute to a faster reduction in carbon intensity and production of low-carbon products.

2 Torrefaction for solid biomass, residue, and unsorted waste materials
Torrefaction, suitable for a wide range of biomass and unsorted waste streams, produces a product, with similar properties to lignite, which can be used in commercially proven lignite gasification units. Lower unit technical costs make torrefaction more attractive for greenfield projects compared with the fast pyrolysis route.

3 Plastic liquefaction for bulk plastic waste
Today, as much as 85% of plastic waste is sent to landfill, incinerated, or left unmanaged, largely because current methods, including mechanical recycling and chemical recycling by pyrolysis, require well-sorted, high-purity plastic waste streams, which are costly and resource-intensive to create.

Plastic liquefaction, however, can take rejected bulk, unsorted plastic waste and convert it into gasification feedstock to produce syngas. As such, it is a complementary recycling method that can contribute significantly to closing the plastic recycling loop and the production of circular plastics.

The plastic pre-conversion process uses a novel plastic liquefaction unit developed as part of a strategic collaboration with Hyundai. This unit can be installed upstream of an existing gasification unit. While the gasifier needs to be adjusted for the new feedstock used, downstream units (syngas treatment, methanol synthesis and methanol-to-olefins units) require no modification. As such, plastic gasification can be deployed quickly and at a relatively low cost.

Technology ready
As demand for lower-carbon and more sustainable products grows, gasification of pre-converted biomass and waste can offer a quick-to-deploy and cost-effective solution that can leverage existing gasification units with only minor adaptions and novel pre-conversion technologies.

Crucially, gasification has the potential to unlock advantaged feeds, such as low-value biomass residues and unsorted plastic waste, and convert them into high-value, bio-based and circular fuels, chemicals, and plastics with attractive margins.

This short article originally appeared in the 2024 ERTC Newspaper, which you can VIEW HERE